Such apparatuses for laser material processing may be used for various purposes, e.g. in the industrial laser material processing. This includes marking or inscribing, removal or structuring processes such as cutting or drilling, sintering (as a rapid prototyping method), and welding.
In various applications of laser material processing, it is preferable to not only guide the position of the laser focus along any desired path but also to simultaneously control the incidence angle of the laser beam axis on the workpiece. Thereby, for example structures of any desired shape may be incorporated into a workpiece, with edges that have a desired inclination angle to the surface of the workpiece. Ideally, the incidence angle should be adjustable independently of the path guiding. The independent adjustment of both of the above parameters should be realizable with high precision and high speed so as to achieve a correspondingly high processing speed in the laser material processing.
This is of special interest for precisely performing drilling processes, for example micro-drilling (∅<500 μm and ∅<200 μm). Holes of such kind are often created by the laser focus being guided along a circular or spiral path (trepanning or spiral drilling). By adjusting the incidence angle of the laser beam axis, holes with a defined conicity may be created.
Document DE 10 2005 047 328 B3 discloses an apparatus for laser beam drilling, comprising a rotating image rotator, a beam manipulator which, when viewed in the beam direction, is arranged in front of the image rotator and serves to adjust the angle and position of the beam relative to the rotation axis of the image rotator, and a focusing device located on the output side of the image rotator. This apparatus is limited in terms of the speed of flexibly adjusting the incidence angle of the laser beam axis on the workpiece and is also limited to drilling holes having a circular shape.
Document DE 10 2010 049 460 A1 further discloses an apparatus for guiding a light beam, in particular a trepanning optic, with two plane-parallel plates that are rotationally driven independently from each other. This device is also limited with regard to the speed of the flexible adjustment of the angle of incidence of the laser beam axis on the workpiece and is largely limited to the drilling of circular holes.
Document EP 1 656 234 B1 shows a scan head as part of a laser drilling and cutting device having a wobble unit for generating a parallel beam displacement. Depending on the setting of this parallel shift, the beam impacts at different distances from the optical axis onto a focusing device, and consequently exits at a corresponding angle from the focusing device. Thus, by adjusting the parallel displacement, an adjustment of the angle of incidence of the laser beam axis on a workpiece may be effected. By arrangement of two plane-parallel optical plates which are rotatable or tiltable about mutually orthogonal axes, a beam offset is accomplished in two directions. Using a scanning block with two mirrors, the laser beam can be guided on a desired path.
The parallel beam offset in plane-parallel plates is especially proportional to the thickness and to the deflection angle of the plane-parallel plate, as a consequence of which relatively thick and hence sluggish plates have to be used for creating large parallel translations and/or have to be rotated by a large angle. The achievable speed in adjusting the laser beam axis and the corresponding processing speed are limited accordingly.